1. Field of the Invention
The present invention relates generally to golf balls. In particular, the present disclosure relates to the composition of a golf ball that includes a highly neutralized polymer having both a high acid content and a high density, without the use of density-adjusting fillers.
2. Description of Related Art
Modern golf balls are known to be made from a variety of polymer materials. The material making up a golf ball may affect the golf ball's performance characteristics in several ways. For example, the selection of the material for use as a golf ball may affect the golf ball's coefficient of restitution, initial velocity off the tee, feel, durability over time, and other properties.
Suitable known materials for use in a golf ball include thermoset materials, such as rubber, styrene butadiene, polybutadiene, isoprene, polyisoprene, and trans-isoprene. Known materials also include thermoplastics, such as ionomer resins, polyamides or polyesters, and thermoplastic polyurethane elastomers. Suitable materials also include polyurea compositions, as well as other materials.
In particular, ionomers are often used for to form the various structural components of known golf balls. For example, ionomers such as Surlyn™ available from E.I. DuPont de Nemours & Company are known to be used for cover layers of golf balls. Other types of ionomers, generally referred to as highly neutralized acid polymers, may also be used in golf balls.
Specifically, highly neutralized acid polymers are known to be used as the material for a golf ball core. For example, U.S. Pat. No. 6,756,436 to Rajagopalan et al., entitled “Golf Balls Comprising Highly-Neutralized Acid Polymers” and filed Apr. 9, 2002, discloses golf balls having highly neutralized acid polymer cores. The disclosure of this application is hereby incorporated by reference. Other conventional highly neutralized acid polymers are generally disclosed in U.S. Pat. No. 7,652,086 to Sullivan et al., entitled “Highly-neutralized Thermoplastic Copolymer Center for Improved Multi-layer Core Golf Ball” and filed Feb. 3, 2006, the disclosure of which is hereby incorporated by reference.
Certain formulations of the highly neutralized acid polymer may affect various physical properties of the polymer material, and so may affect the play characteristics of a golf ball made from that material. For example, U.S. Pat. No. 5,688,869 to Sullivan, entitled “Golf Ball Cover Compositions” and filed Jun. 21, 1995, discloses that highly neutralized acid polymers having high acid content (greater than 16% by weight) may achieve increased hardness, modulus, and resilience characteristics. These properties of high acid highly neutralized polymers may be advantageous to golf ball covers, cores, or other structural components, in order to achieve desired play characteristics.
Additionally, various additives and fillers may be added to a polymer composition in order to affect the material's properties. U.S. Pat. No. 7,402,114 to Binette et. al, entitled “Highly Neutralized Polymer Material with Heavy Mass Fillers for a Golf Ball” and filed on Jan. 15, 2007, discloses a golf ball with a layer formed from a highly neutralized polymer that has been weighted using density-adjusting fillers. Broadly, the fillers may be used to adjust the properties of the golf ball layer, reinforce the layer, or for any other purpose. As is generally known, fillers may be included in a polymer material making up a golf ball in order to change (for example) the weight or moment of inertia of a golf ball.
However, it is also known that highly neutralized acid polymers having high acid content may exhibit various disadvantages. For example, high acid content may result in the material having increased polarity, making the material less compatible with potential blend materials. U.S. Pat. No. 7,767,759 to Kim, entitled “Composition for Use in Golf Balls” and filed on Jul. 14, 2005, discuses this problem. The disclosure of U.S. Pat. No. 7,767,759 is hereby incorporated by reference. This problem, and other manufacturing difficulties associated with high acid content, are also discussed in U.S. Pub 2008/0312007 to Rajagopalan et al., entitled “Highly Neutralized Polymeric Composition for Golf Ball Layers” and filed on May 20, 2008, the disclosure of which is hereby incorporated by reference.
Such compatibility problems may result in golf ball layers that are less consistent and less uniform than may be desired. Namely, for example, such compatibility problems may result in an irregular dispersion of fillers in the polymer material. The golf ball manufactured from this material may accordingly exhibit play characteristics that are not highly consistent from shot to shot. Therefore, the use of fillers to control the weight or moment of inertia in a golf ball layer made from a highly neutralized polymer material may be difficult when the highly neutralized polymer has a high acid content.
Therefore, there exists a need in the art for highly neutralized acid polymer materials having a high acid content that allow for control over the various physical properties of the golf ball.